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62 GOLF COURSE MANAGEMENT 07.17
influence of predetermined variables (treat-
ments). Every month during the experiment,
a soil probe with a 4-inch diameter was used
to collect 10 soil cores at random from the
monitored area of each fairway. The collected
soil cores were examined in the laboratory for
larvae and/or pupae. A minimal number of
larvae/pupae specimens were collected during
this experiment, similar to previously docu
-
mented results in the literature. No mean-
ingful data could be derived from the larval
populations, and therefore no larval data are
presented in this report.
Results and discussion
The number of billbug adults recovered
from the pitfall traps varied significantly be
-
tween the two sites. In 2015, a total of 876
billbugs were recovered at CCC, which was
more than five times the number found at
CCMO (Figure 4). In 2016, a total of 158
billbugs were found at CCMO, which was
comparable to the amount found the previous
year. At CCC, however, a total 1,077 billbugs
were found in 2016, indicating a 22% popu
-
lation increase over 2015. It is worth noting
that the areas installed with pitfall traps ac
-
counted for only 0.11% of the total area where
insecticide applications were withdrawn. It is
therefore reasonable to speculate that real bill
-
bug populations present at both fairways were
much higher than indicated by the numbers
trapped. The variation between the two sites
is likely a reflection of multiple factors, includ
-
ing whether the roughs — 20 feet away from
the monitored areas on both fairways — were
regularly treated with insecticides.
On the two fairways, hunting billbug ap
-
peared to be the dominant species (Figure
4). At CCC, bluegrass billbugs collected ac
-
counted for 13.7% and 9% of the population
in 2015 and 2016, respectively. At CCMO,
however, we found only six bluegrass billbugs
in 2015 and none in 2016. Previous research
demonstrated that both billbug species can
survive on a wide range of turfgrass species,
including tall fescue (Festuca arundinacea
Schreb.) and Kentucky bluegrass, the pri
-
mary grass species for roughs, and zoysiagrass,
the species for fairways at the two sites (3,6).
However, why such a discrepancy in popula
-
tion composition was found at the two fair-
ways, even though the turfgrass species at
both sites were comparable, is unclear.
Despite the difference in population size
and composition, activity of billbug adults at
Billbug count, April 2015
Figure 3. Pitfall traps installed on zoysiagrass fairways of Columbia Country Club (top) and Country Club of Missouri
(bottom) in April 2015. Photos by Brett Loman